This paper describes measured temperature profiles and thermal stratification in eight aircraft hangar buildings during the heating season. Presented also is the predicted impact of thermal stratification on heating energy requirements. The hangar buildings included two main ceiling heights (9.35 and 17.1 m (31 and 56 ft)), two ceiling types (fiat and Quonset), two types of heating systems (vertical discharge forced warm air and downdraft convective unit heaters), and various types of large external doors. Measured stratification, expressed by floor-to-ceiling temperature differential, is in the range 4--11 °C (7 .2-20 °F). Two air layers existed in the hangar bay area, a warm upper air layer and a cooler lower air layer. The lower air layer (up to 2 m (7 ft) high from the floor) is characterised by a steep vertical temperature gradient in the range 0.8-2.6 °C/m (0.4-1.4 °F/ft). In the upper air layer, above 2 m, the vertical temperature gradient shallows considerably to 0.5 °CIm (0.3 °F/ft). Results indicate that thermal stratification can have a significant impact on the building's heating energy requirements. In the hangar buildings studied, predicted excess heating energy requirements due to 8 °C floor-to-ceiling temperature differential can be as much as 38% as compared to the case with no stratification.